Method of refining in improved Q-BOP vessel

ABSTRACT

A Q-BOP steelmaking vessel construction in which tuyeres extending through the bottom wall of the vessel for delivering oxygen to the bath have a diameter not more than 1/13 of the depth of the bath in the converter and the total cross-sectional area of all oxygen tuyeres in the converter in square centimeters is from one to three times the heat size expressed in metric tons.

"United States Patent Brisse et al.-

[ Sept. 23, 1975 METHOD OF REFINING IN IMPROVED Q-BOP VESSEL Inventors: Andre H. Brisse, Pittsburgh; David K. Griffiths, Penn Hills Twp., Allegheny County, both of Pa.

United States Steel Corporation, Pittsburgh, Pa.

Filed: Dec. 5, 1973 Appl. No.: 421,883

Related US Application Data Division of Ser. No. 284,693, Aug. 29, 1972, Pat. No. 3,802,685.

Assignee:

US. Cl. 75/60; 75/93 E Int. Cl. C21C 5/34; C21C 7/00 Field of Search 75/59, 60, 93 E; 164/56 References Cited UNITED STATES PATENTS 11/1943 Lellep 75/60 3,706.549 12/1972 Knuppel et a1. 7. /60 3,771.998 11/1973 Knuppel et a1. i. 75/60 X 3,793,001 2/1974 Ramacciotti 75/60 Primary Examiner-Allen B, Curtis Assistant Examiner-Thomas A. Waltz Attorney, Agent, or Firm-David S. Urey 1 Claim, 1 Drawing Figure US Patent Sept. 23,1975 3,907,549

.METHOD OF REFINING IN INIPROVED Q-BOPi This is a division ofapplication ser. 'No. 284,6 93,

the vessel. Each tuyere comprises an oxygen inlet tube.

surrounded by alarger-concentric inlet tube for the simultaneous injection of a jacket gas, which does not re act, or reacts only slowly with the molten metal in'the bathand the material from which the nozzle is constructcd. This jacket gas acts as a coolant reducing the rate of reaction between the molten metal and the oxygen adjacent to the tuyere, preventing rapid erosion of the tuyere, and reducing the rate of erosion of the lining in the vessel bottom. Thus, the furnace lining and the tuyere wear at the same rate.

South African Patent No. 691,280 teaches that the total cross-sectional area of oxygen delivering tuyere pipes in square centimeters should be approximately equal to the weight of pig iron charged into the converter in metric tons. The same reference teaches that the greatest allowable tuyere diameter for vertically mounted tuyeres should not exceed 1/35 of the depth of the bath, assuming an oxygen pressure of about 5 to atmospheres.

We have discovered that not only can larger tuyeres be used in a bottom blown process, but by increasing the diameter of the tuyeres to l/l5 of the bath depth, the number of tuyeres required in a given vessel is only one-third the number required if the diameter is 1/35 of the bath depth. This results not only in a reduced re-" quirement in number of tuyeres, but also in a reduced number of piping connections for both oxygen and jacketing gas since fewer tuyeres are required. This, in

turn, results in a decreased manpower requirement for maintenance and periodic replacement of parts.

It is the principal object of our invention to provide improved apparatus for refining molten metal in a Q-BOP steelmaking vessel.

It is another object of our invention to provide apparatus having increased tuyere size over what was heretofore possible.

These and other objects will be more readily apparent with reference to the following detailed specification and the appended drawing in which:

The single FIGURE is a vertical, cross-sectional view of a Q-BOP steelmaking vessel.

A bottom blown oxygen steelmaking vessel 10 has a removable bottom 12, comprising a bottom plate 14, and one or more generally upstanding tuyeres 16, which are surrounded by refractory material 18. The bottom plate 14 is fastened to the furnace by bolts 20. The sides of the refractory portion of the removable bottom do not contact the refractory lining 22 of the vessel, but sufficient clearance is provided around the,

bottom for inserting a refractory gunning mixture 24 to provide a metal and slag tight seal.

Tuyere 16 is a dual concentric tuyere composed of an inner tube 30 and an outer tube 34. Tube 30 is spaced from tube 34 by spacers 36, which may be weld beads,

spiral wound wire, or any other suitable means for maintaining concentricity. The inner or central tube 30 delivers oxygen and lime to the molten metal bath. The

dard circular,- cross-sectional tuyere to, about l/,15 of the bath depth apparently reduces the height of the jet of gas in the bath and thus reduces the tendency of spit ting to occur inthebath. We have also-found that the totalcrossssectional area-of all oxygen. delivering tu-. yeres in square-centimeters maybe from oneto three times the ba ch size in metric tons. a

Thetuyere need not be a standard circular tuyere,

. but 'mayhave any of a number of cross-sectional shapes .such as square, rhombic, rectangular,=. ellipse, oval,

pointed ellipse, or any other desired shape. Todefine a common parameter of such shapes, we must-;turn to the terminology of fluid mechanics, wherein the hydraulic radius of a non-circular duct is the fluid-filled area divided by the inside perimeter of the duct. The hydraulic diameter equals four times the hydraulic radius. As above, a tuyere of any cross section having a hydraulic diameter up to about l/l3 the bath depth is operable in our invention.

The following examples illustrate the operability of our invention.

EXAMPLE I Circular oxygen tuyere pipes 2.86 centimeters in diameter have been employed in a Q-BOP vessel in which the bath depth was approximately 28 inches (71.1 centimeters). The hydraulic diameter was l/25 the bath depth. Six tuyeres, having a total crosssectional area of the oxygen pipe of 38.5 square centimeters, were used to blow oxygen into a bath of 18.2 metric tons. Thus, the cross-sectional area of the oxygen-delivering tuyeres was 2.11 times the bath size in metric tons.

EXAMPLE ll Circular oxygen tuyere pipes having an internal diameter of 2.323 inches (5.9 centimeters) were employed in a Q-BOP vessel in which the bath depth was 32 inches (81.3 centimeters). The hydraulic diameter was 1 14 the bath depth. Two tuyeres having a total cross-sectional area of the oxygen pipe of 52.8 square centimeters were used to blow oxygen into a bath of 23 metric tons. The cross-sectional area of the oxygendelivering tuyeres was 2.3 times the bath size in metric tons. Oxygen flow was 1400 scfm (2352 Nm lhr.) at 15 psig.

Our invention comprehends the broad range of hydraulic diameters from about 1 inch to 2.85 inches or 2.5 centimeters to 7.5 centimeters. However, we prefer a hydraulic diameter in the range of about 1.6 to 2.5 inches or 4.0 to 6.5 centimeters. We prefer a large hydraulic radius since it will accommodate low pressures. Low oxygen pressures required large tuyeres to obtain sufficient oxygen throughput to operate the refining process. Of course the pressure must be sufficient to overcome the ferrostatic head of molten metal in the vessel. We have found that the oxygen pressure must be maintained at a minimum of 1 atmosphere and can be as high as 15 atmospheres. The oxygen throughput must be at least normal cubic meters per hour per square centimeter of oxygen tuyere cross section.

The tuyere pipes may be installed at an angle with respect to the axis of the Q-BOP converter vessel to improve mixing or impart rotation to the bath thus, minimizing sloshin'g'an'd'bath instability. ln this case, tu-

yeres of even larger crossse'ction'al area may be used.

A method ofrefining a bath of molten metal in a Q-BOp steelmaking .vessel comprising:

For instance, the tuyere diameter maybe'increased about for nozzles inclined'30 to the vessels vertical axis. The tuyere pipes may also be installed in the sidewall of the converter beneath moltenmetal bath; i

From the foregoing it is readily-apparentthat we have invented an improved Q-BOP vessel for refining molten 'the surface of'the metal in which tuyeres extending throughthe bottom wall of the vessel have a hydraulic diameter no greater than l/13 of the bath depth and a total cross-sectional area of the oxygen delivering portion of such tuyeres in metric tons. We claim:

square centimeters from l to 3 times the bath size in introducing oxygen through generally upstanding tuyeres in the bottom of the vessel having a hydraulic diameter from 1/25 to l/l3 of the bath depth and having a total cross-sectional area'of all such tuyeres in square centimeters from one to three times thebath size in metric tons at a minimum rate of.

refine said molten metal bath, 

1. A METHOD REFINING A BATH OF MOLTEN METAL IN A Q-BOP STEELMAKING VESSEL COMPRISING: INTRODUCING OXYGEN THROUGH GENERALLY UPSTANDING TUYERES IN THE BOTTOM OF THE VESSEL HAVING A HYDRAULIC DIAMETER FROM 1/25 TO 1/13 OF THE BATH DEPTH AND HAVING A TOTAL CROSSSECTIONAL AREA OF ALL SUCH TUYERES IN SQUARE CENTIMETERS FROM ONE TO THREE TIMES THE BATH SIZE IN METRIC TONS AT A MINIUMM RATE OF ABOUT 85 NM3/HOUR/SQUARE CENTIMETER OF TUYERE CROSS- SECTION AT A MINIUM PRESSURE OF 1 ATMOSPHERE TO THE MOLTEN METAL BATH CONTAINED IN SAID VESSEL, AND MAINTAINING THE OXYGEN PRESSURE BETWEEN FROM 1 TO 15 ATMOSPHERES FOR A SUFFICINT PERIOD OF TIME TO REFINE SAID MOLTEN METAL BATH. 